Search NASA⌕ Search

SEARCH · Search NASA

Results for “Aries”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Performance considerations of frequency-hopping multiple access

The basic system parameters of a frequency-hopping multiple-access system are investigated. Noncoherent binary FSK and M-ary FSK signal formats are studied in a random-access asynchronous environment. Both slow and fast frequency hopping are considered. Under relatively ideal conditions, the degradation in performance with respect to the number of users is determined. The dependence on performance due to hopping rate and bandwidth constraint is developed. It is shown, for example, that, for fast hopping, the optimum hopping rate is that which spreads the users' power over the entire available bandwidth during each baud time. This agrees with the basic spread spectrum philosophy of making the signal appear white over as wide a bandwidth as possible. The computational results describe the trade-off between the number of tones in M-ary FSK and the number of hops per symbol. Given a specified number of tones in the frequency-hopping system, the results describe the manner in which the system degrades as the number of users is increased.

Weber, C. L.↗
NASA NTRS1983

A class of nonideal solutions. 1: Definition and properties

A class of nonideal solutions is defined by constructing a function to represent the composition dependence of thermodynamic properties for members of the class, and some properties of these solutions are studied. The constructed function has several useful features: (1) its parameters occur linearly; (2) it contains a logarithmic singularity in the dilute solution region and contains ideal solutions and regular solutions as special cases; and (3) it is applicable to N-ary systems and reduces to M-ary systems (M or = N) in a form-invariant manner.

Zeleznik, F. J.↗
NASA NTRS1984

A solar spectral line list between 10 and 200 A modified for application to high spectral resolution X-ray astronomy

A spectral line list for the 10-200 A range is developed from existing solar spectra for application to high spectral resolution measurements of astrophysical plasmas. The solar spectral line lists are merged into a single comprehensive list. The effect of the solar emission measure distribution is removed from the line intensities, which results in a set of emission rates for the lines that can be applied to many optically thin, low density high temperature plasmas in ionization equilibrium. In addition to the measured solar lines, 250 theoretical lines are added to this list. These lines fall in wavelength regions where the existing solar lists have few lines because of limitations in instrumental sensitivity. Also, some lines have been added because the sun has very little plasma at temperatures of about one million K, and consequently these lines are weak or absent in solar spectra. The entire list contains about 600 lines. Finally, predicted spectra of the two RS CVn stars, alpha Aur (Capella) and UX Ari, are presented at 1 and 0.25 A spectral resolution. Also, the solar spectrum is shown at 1 A resolution, and the emission rate spectrum (spectrum not modified by an emission measure distribution) is shown at very high spectral resolution. The predicted spectra for Capella and UX Ari are based on results obtained from the Einstein and International Ultraviolet Explorer (IUE) spacecraft.

Doschek, G. A.↗
NASA NTRS1985

Dual polarization VLBI observations of stellar binary systems at 5 GHz

The binary systems Sigma CrB, SZ Psc, HR 1099, UX Ari, HR 5110, Algol, and Cyg X-1 are characterized in terms of marcsec-scale radio structure on the basis of dual-polarization observations at 4.969-4.997 GHz, obtained with an international VLBI array comprising the 100-m Effelsberg, 36-m Haystack, 42-m Green Bank, 26-m Fort Davis, 130-m-equivalent VLA, and 40-m Owens Valley telescopes (system temperatures 40-70 K) at 22-14 h UT on July 26-27, 1983. The data are presented in graphs and tables and discussed in detail. Single Gaussian brightness distributions with theta(FWHM) = 0.5-2.0 marcsec and brightness temperatures (2-200) x 10 to the 8th K are determined for four sources; core-halo structures are found for UX Ari and Algol; and an upper limit of 50 microarcsec is established for the angular separation of the regions of left and right circular polarization. The gross features seen in RS CVn systems are explained in terms of a simple expanding-coronal-loop model of flare events.

Mutel, R. L.↗
NASA NTRS1987

SP-100 control system modeling

SP-100 Control Systems modeling was done using a thermal hydraulic transient analysis model called ARIES-S. The ARIES-S Computer Simulation provides a basis for design, integration and analysis of the reactor including the control and protection systems. It is a modular digital computer simulation written in FORTRAN that operates interactively in real time on a VAX minicomputer.

Meyer, R. A.↗
NASA NTRS1989

Generalized Multiple-Trellis-Coded Modulation

Generalized multiple-trellis-coded modulation technique combines multiple trellis coding (more than one channel symbol per trellis branch transmitted) with symmetrical M-ary phase-shift keying. Transmitter puts out k M-ary code symbols for every b input binary symbols. Throughout performances, b/k, of trellis-coded multiple-phase-shift-keying channels compared with computational cutoff rates, R0, of multiple-phase-shift keying. Performs better than conventional trellis-coded modulation technique, with no increase in complexity.

Divsalar, D.↗
NASA NTRS1990

Apparent orbit of the spectroscopic binary Beta Arietis with the time Mark III Stellar Interferometer

The spectroscopic binary Beta Ari has been directly resolved with the Mark III Stellar Interferometer. Observations in 1988 were analyzed to determine the visual orbit of the system with the following results: eccentricity = 0.903 +/- 0.012, semimajor axis = 0.0361 +/- 0.0003 arcsec, inclination = 44.7 +/- 1.3 deg, longitude of periastron = 209.1 deg +/- 1.2 deg, position angle of ascending node = 79.1 deg +/- 0.8 deg. The measured magnitude difference between two components, Delta m = 2.63 +/- 0.22 at 800 nm, yields individual visual magnitudes of m(v1) = 2.70 +/- 0.02 and m(v2) = 5.80 +/- 0.20. Combined with data from spectroscopic observations, masses M1 = (2.34 +/- 0.10) solar masses, M2 = (1.34 +/- 0.07) solar masses, and geometrical parallax pi = 0.053 arcsec +/- 0.002 arcsec are derived. These results demonstrate that both components of Beta Ari agree well with the empirical mass-luminosity relation.

Pan, X. P.↗
NASA NTRS1991

The analysis of a rocket tomography measurement of the N2+3914A emission and N2 ionization rates in an auroral arc

Techniques were developed for recovering two-dimensional distributions of auroral volume emission rates from rocket photometer measurements made in a tomographic spin scan mode. These tomographic inversion procedures are based upon an algebraic reconstruction technique (ART) and utilize two different iterative relaxation techniques for solving the problems associated with noise in the observational data. One of the inversion algorithms is based upon a least squares method and the other on a maximum probability approach. The performance of the inversion algorithms, and the limitations of the rocket tomography technique, were critically assessed using various factors such as (1) statistical and non-statistical noise in the observational data, (2) rocket penetration of the auroral form, (3) background sources of emission, (4) smearing due to the photometer field of view, and (5) temporal variations in the auroral form. These tests show that the inversion procedures may be successfully applied to rocket observations made in medium intensity aurora with standard rocket photometer instruments. The inversion procedures have been used to recover two-dimensional distributions of auroral emission rates and ionization rates from an existing set of N2+3914A rocket photometer measurements which were made in a tomographic spin scan mode during the ARIES auroral campaign. The two-dimensional distributions of the 3914A volume emission rates recoverd from the inversion of the rocket data compare very well with the distributions that were inferred from ground-based measurements using triangulation-tomography techniques and the N2 ionization rates derived from the rocket tomography results are in very good agreement with the in situ particle measurements that were made during the flight. Three pre-prints describing the tomographic inversion techniques and the tomographic analysis of the ARIES rocket data are included as appendices.

Mcdade, Ian C.↗
NASA NTRS1991

On linear structure and phase rotation invariant properties of block M-PSK modulation codes

Two important structural properties of block M(=2')-ary PSK modulation codes, linear structure and phase symmetry, are investigated. An M-ary modulation code is first represented as a code with symbols from the integer group S(MPSK) = (0,1,2,...M-1) under modulo-M addition. Then the linear structure of block MPSK modulation codes over S(M-PSK) with respect to modulo-M vector addition is defined, and conditions are derived under which a block MPSK modulation code is linear. Once the linear structure is developed, the phase symmetry of block M-PSK modulation codes is studied. In particular, a necessary and sufficient condition for a block MPSK modulation code that is linear as a binary code to be invariant under 2 h 180 deg/M phase rotation (for h = 1 to l) is derived. Finally, a list of short 8PSK and 16PSK modulation codes is given, together with their linear structure and the smallest phase rotation for which a code is invariant.

Kasami, Tadao↗
NASA NTRS1992

Investigation of Bandwidth-Efficient Coding and Modulation Techniques

The necessary technology was studied to improve the bandwidth efficiency of the space-to-ground communications network using the current capabilities of that network as a baseline. The study was aimed at making space payloads, for example the Hubble Space Telescope, more capable without the need to completely redesign the link. Particular emphasis was placed on the following concepts: (1) what the requirements are which are necessary to convert an existing standard 4-ary phase shift keying communications link to one that can support, as a minimum, 8-ary phase shift keying with error corrections applied; and (2) to determine the feasibility of using the existing equipment configurations with additional signal processing equipment to realize the higher order modulation and coding schemes.

Osborne, William P.↗
NASA NTRS1991

Programmable digital modem

The design of the Programmable Digital Modem (PDM) is outlined. The PDM will be capable of operating with numerous modulation techniques including: 2-, 4-, 8- and 16-ary phase shift keying (PSK), minimum shift keying (MSK), and 16-ary quadrature amplitude modulation (QAM), with spectral occupancy from 1.2x to 2x the data symbol rate. It will also be programmable for transmission rates ranging from 2.34 to 300 Mbit/s, where the maximum symbol rate is 75 Msymbol/s. Furthermore, these parameters will be executable in independent burst, dependent burst, or continuous mode. In dependent burst mode the carrier and clock oscillator sources are common from burst to burst. To achieve as broad a set of requirements as these, it is clear that the essential signal processing must be digital. In addition, to avoid hardware changes when the operational parameters are changed, a fixed interface to an analog intermediate frequency (IF) is necessary for transmission; and, common system level architectures are necessary for the modulator and demodulator. Lastly, to minimize size and power, as much of the design as possible will be implemented with application specific integrated circuit (ASIC) chips.

Poklemba, John J.↗
NASA NTRS1992

Coded 16-CPFSK for downlink applications

A bandwidth-efficient constant-envelope Proof-of-Concept (POC) modem is described. The modem was developed on an Advanced Modulation Techniques Development contract for the NASA/Lewis Research Center. The POC modem employs 16-ary Continuous Phase Frequency Shift Keying (16-CPFSK) modulation. The 16 frequencies are spaced every 1/16th baud rate which produces a compact spectrum allowing 2 bits/sec/Hz operation. The modem is designed for 200 mb/s Time Division Multiple Access (TDMA) application with 100 MHz adjacent channel spacing. Overall rate 3.4 convolutional coding is incorporated. The demodulator differs significantly from typical quadrature phase detector approaches in that phase is coherently measured by processing the baseband output of a frequency discriminator. Baud rate phase samples for the baseband processor are subsequently decoded to yield the original data stream. The method of encoding onto the 16-ary symbol-ending phase nodes, together with convolutional coding gain, results in near Quadrature Phase Shift Keying (QPSK) theoretical performance. The modulated signal is of constant envelope; thus the power amplifier can be saturated for peak performance. The spectrum is inherently bandlimited and requires no RF filter for sidelobe containment. Two novel theoretical techniques are used in this 16-CPFSK modem: (1) coherent phase measurements are obtained by processing an FM discriminator baseband output; and (2) modulation is accomplished via a closed-loop-linearized voltage controlled oscillator (VCO).

Davis, Robert↗
NASA NTRS1994

From Undersea to Outer Space: The STS-40 Jellyfish Experiment

This is an educational production featuring 'Ari', animated jellyfish who recounts his journey into space. Jellyfish were flown aboard the shuttle to study the effects of microgravity on living organisms. Topics Ari explores are: microgravity, life sciences, similarities between jellyfish and humans, and the life cycle and anatomy of a jellyfish.

Source record↗
NASA NTRS1995

High temperature structure in cool binary stars

Strong high temperature emission lines in the EUVE spectra of binary stars containing cool components (Alpha Aur (Capella), 44 iota Boo, Lambda And, and VY Ari) provide the basis to define reliably the differential emission measure of hot plasma. The emission measure distributions for the short-period (P less than or equal to 13 d) binary systems show a high temperature enhancement over a relatively narrow temperature region similar to that originally found in Capella (Dupree et al. 1993). The emission measure distributions of rapidly rotating single stars 31 Com and AB Dor also contain a local enhancement of the emission measure although at different temperatures and width from Capella, suggesting that the enhancement in these objects may be characteristic of rapid rotation of a stellar corona. This feature might be identified with a (polar) active region, although its density and absolute size are unknown; in the binaries Capella and VY Ari, the feature is narrow and it may arise from an interaction region between the components.

Dupree, A. K.↗
NASA NTRS1996

STS-79 Flight Day 6

On this sixth day of the STS-79 mission, the flight crew, Cmdr. William F. Readdy, Pilot Terrence W. Wilcutt, Mission Specialists, Thomas D. Akers, Shannon Lucid, Jay Apt, and Carl E. Walz, continue activities aboard Atlantis/Mir as the nine astronauts and cosmonauts work in their second full day of docked operations. The continuing transfer of logistical supplies and scientific hardware can be seen proceeding smoothly. Apt and Walz once again worked with the Active Rack Isolation System experiment to replace a broken pushrod. With that complete, Apt monitors the ARIS experiment as Readdy and Korzun fire small maneuvering jets on their spacecraft to test the ability of ARIS to damp out any disturbances created by the firings. Walz also is continuing his work with the Mechanics of Granular Materials experiment in Atlantis' double Spacehab module. The astronauts used the large format IMAX camera to conduct a photographic survey of Mir from the Shuttle's flight deck windows while Akers shot IMAX movie scenes of Readdy, Wilcutt, and Korzun in the Spektr module.

Source record↗
NASA NTRS1996

STS-79 Flight Day 3

On this third day of the STS-79 mission, the flight crew, Cmdr. William F. Readdy, Pilot Terrence W. Wilcutt, Mission Specialists, Thomas D. Akers, John E. Blaha, Jay Apt, and Carl E. Walz, start another busy day on orbit activating experiments in the Spacehab module. Readdy and Wilcutt are seen conducting two rendezvous burns while other crew members are seen working in the Spacehab module. The Active Rack Isolation System, or ARIS, is tended to by Walz, who performs a minor maintenance procedure on one of ARIS' vibration-damping pushrods while Akers works with an inventory management system using a bar code reader to more effectively keep track of items that will be transferred back and forth between the Shuttle and the Mir. Apt continues work with a furnace which heats to nearly 1,600 degrees centigrade to melt metal samples for study after the flight. Apt also provides a television tour of the Spacehab, which is twice its normal size for this flight to allow extra room for science experiments and logistical items slated for transfer to Mir.

Source record↗
NASA NTRS1997

Testing and Implementation of Advanced Reynolds Stress Models

A research program was proposed for the testing and implementation of advanced turbulence models for non-equilibrium turbulent flows of aerodynamic importance that are of interest to NASA. Turbulence models that are being developed in connection with the Office of Naval Research ARI in Non-equilibrium are provided for implementation and testing in aerodynamic flows at NASA Langley Research Center. Close interactions were established with researchers at Nasa Langley RC and refinements to the models were made based on the results of these tests. The models that have been considered include two-equation models with an anisotropic eddy viscosity as well as full second-order closures. Three types of non-equilibrium corrections to the models have been considered in connection with the ARI on Nonequilibrium Turbulence: conducted for ONR.

Speziale, Charles G.↗
NASA NTRS1998

Final Report

This grant was made to fund two accepted proposals to observe with the ASCA satellite: (1) Debunking the myth of two-temperature coronae of active stars, and (2) Dynamic coronae of dMe stars. We obtained the requested observations and have now completed two papers that will be published in the Astrophysical Journal. The RS CVn binary star UX Ari was observed for 14 hours with all four detectors onboard the ASCA satellite. The X-ray emission was at a constant, quiescent level during the first 12 hours, after which time a powerful flare with a peak luminosity of 1.4 x 10(exp 32) ergs/s started. The flare was observed until shortly after its peak. We present a spectral and temporal analysis of the UX Ari observations and analyze the data with a two-ribbon flare model including estimates for cooling losses. A time-dependent reconstruction of the emission measure (EM) distribution shows that two separate plasma components evolve during the flare (one being identified with the quiescent EM). Most of the flare EM reaches temperatures between 50 MK and 100 MK or more. Magnetic confinement requires the loop arcade to be geometrically large, with length scales on the order of one stellar radius. The electron densities inferred from the model decrease from initial values around 10(exp 12)/cc early in the flare to about 10(exp 11)/cc at the flare peak. The best-fit models require surface magnetic field strengths of a few hundred G, compatible with the maximum photospheric fields expected from equipartition. The flare parameters imply a (conductive and radiative) cooling loss time of less than one hour at flare peak. The elemental abundances increase significantly during the flare rise, with the abundances of the low-FIP elements Fe, Mg, Si, and Ni typically increasing to higher levels than the high-FIP elements such as S or Ne. The Fe abundance increases from (17 +/- 4)% of the solar photospheric value during quiescence up to (89 +/- 18)% at flare peak. A fractionation process that occurs during the chromospheric evaporation phase may selectively enrich low-FIP elements as in the solar corona; alternatively, the chromospheric evaporation may itself bring metal-rich plasma into the metal-poor corona.

Linsky, Jeffrey L.↗